Not applicable
1. Field of the Invention
The present invention relates to hydrogenation catalysts. More particularly, the present invention relates to hydrogenation catalysts for olefins.
2. General Background of the Invention
Among homogenous hydrogenation catalysts, the most widely used are RhCl(PPh3)3 (Wilkinson""s catalyst)1 and [Ir(cod)(py)(PCy3)]PF6 [py=pyridine; cod=cyclooctadiene] (1, Crabtree""s catalyst)2. The latter complex is an efficient catalyst for polysubstituted olefins lacking coordinating functionalities and is particularly useful in directed hydrogenation processes.3 Despite having such remarkable catalytic activity, 1 has been shown to be susceptible to deactivation through the formation of inactive hydride-bridged trimer [(Ir(py)(PCy3)(H2))3(xcexc3-H)]PF6, and has also been demonstrated as thermally unstable.2a,c 
Nucleophilic N-heterocyclic carbenes, or so-called xe2x80x9cphosphine mimicsxe2x80x9d, have attracted considerable attention as possible alternatives for the widely used phosphine ligands in homogeneous catalysis.4 Indeed, the inventors and others had found that the replacement of bulky phosphines with sterically demanding N-heterocyclic carbenes IPr (IPr=1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) (see FIG. 2) or IMes (IMes=1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) (see FIG. 1) can result in significant catalytic performance in olefin metathesis,5 Cxe2x80x94C bond formation reaction,6 animation of aryl chlorides,7 hydrogenation8 and hydroformylation9.
The following U.S. patent is incorporated herein by reference: U.S. Pat. No. 5,728,839 for xe2x80x9cMetal complexes with heterocycles carbenesxe2x80x9d and all references recited therein and herein.
Also incorporated by reference is the paper which describes an embodiment of the present invention, which was attached to U.S. Provisional patent application serial No. 60/251,075, filed Dec. 4, 2000, under the title xe2x80x9cA Cationic Iridium Complex Bearing an Imidazolidine-2-ylidene Ligand as Alkene Hydrogenation Catalystxe2x80x9d, and which was published in Organometallics (2001), vol. 20, no. 6, pp. 1255-1258 under the title: xe2x80x9cA Cationic Iridium Complex Bearing an Imidazol-2-ylidene Ligand as Alkene Hydrogenation Catalystxe2x80x9d.
In view of these findings and in their continued search for more efficient and stable catalysts, the inventors turned their attention to the Crabtree-type iridium hydrogenation catalyst. The inventors wished to examine whether the replacement of PCy3 with SIMes (1,3-dimesityl-4,5-dihydroimidazol-2-ylidene or related n-heterocyclic carbenes, which is trivially called herein saturated IMes or SIMes) (see FIG. 3) in 1 could lead to the generation of a more active and more thermally tolerant hydrogenation catalyst. The present inventors now report the synthesis of a new iridium carbene complex [Ir(cod)(py)(SIMes)]PF6 (2) and its catalytic behavior in the hydrogenation of olefins.
Attached to U.S. Provisional Patent Application Serial No. 60/289,073 and incorporated herein by reference is a copy of a manuscript entitled xe2x80x9cCationic Iridium Complexes Bearing Imidazol-2-ylidene Ligands As Transfer Hydrogenation Catalystsxe2x80x9d which describes work on transfer hydrogenation using an Iridium catalyst. This paper has appeared in print as xe2x80x9cCationic Iridium Complexes Bearing an Imidazolidine-2-ylidene Ligand as Transfer Hydrogenation Catalysts.xe2x80x9d Hillier, A. C.; Lee, H. M.; Stevens, E. D.; Nolan, S. P. Organometallics, 2001, 20, 4246-4252. This is complementary to our earlier work involving hydrogenation with dihydrogen described in the paper which describes an embodiment of the present invention, which was attached to U.S. Provisional patent application serial No. 60/251,075, filed Dec. 4, 2000, under the title xe2x80x9cA Cationic Iridium Complex Bearing an Imidazolidine-2-ylidene Ligand as Alkene Hydrogenation Catalystxe2x80x9d, and which was published in Organometallics (2001), vol. 20, no. 6, pp. 1255-1258 under the title: xe2x80x9cA Cationic Iridium Complex Bearing an Imidazol-2-ylidene Ligand as Alkene Hydrogenation Catalystxe2x80x9d. Both of these papers, and all references recited therein, are also incorporated herein by reference.
The present invention includes hydrogenation with H atom sources other than hydrogen gas. This is what is so special about this discovery. Other examples exist but this is a fairly active system.
The present invention includes hydrogenation with dihydrogen and transfer hydrogenation (alcohols are source of H atoms).
The Ir catalysts described herein perform catalytic transfer hydrogenation using an inexpensive alcohol as the H atom source. The systems are versatile, hydrogenating both ketones and olefin. Very low catalyst loadings are required. The systems are very tolerant to elevated temperatures. The systems bear a nucleophilic carbene as ancillary ligand which affords a steric and electronic handle on the catalyst activity.
The present invention allows for either hydrogenation or transfer hydrogenation using inexpensive alcohols as the H atom source. The present catalyst systems allow both to be performed within essentially the same framework.
The new cationic iridium carbene complex [Ir(cod)(py)(SIMes)]PF6 (2) has been synthesized by reaction of [Ir(cod)(py)2]PF6 with SIMes. Complex 2 is an active hydrogenation catalyst capable of hydrogenating simple olefins at room temperature and atmospheric pressure of hydrogen.
The cationic iridium carbene complexes [Ir(cod)(N)(L)]X have been synthesized by reaction of [Ir(cod)(py)2]PF6 with L or NL ligands. Complexes of this type are active hydrogenation catalysts capable of hydrogenating simple olefins at room temperature and atmospheric pressure of hydrogen or by transfer hydrogenation.
The present invention includes an iridium carbene complex of the formula [Ir(diene)(N)(L)]X. where diene is a diene or two monoene, N is a 2 electron nitrogen donor, L is a bulky nucleophilic carbene, and X is an anionic counterion. This complex is preferably prepared by a simple ligand exchange reaction of [Ir(diene)(N)2]X with L in toluene. Preferably an excess of L is used. The L can be prepared and used in situ by the reaction of L.HCl with KOBut in THF, and the free carbene can be extracted with toluene and treated with [Ir(cod)(py)2]PF6 or equivalent precursors directly.
This complex can be used as a catalyst in a hydrogenation reaction in a method of hydrogenating simple olefins, comprising: The reaction can occurs at a pressure of 0.1 to 150 atmosphere and a temperature of 0-150xc2x0 C.; for example, the reaction can occurs at a pressure of about 1 atm and a temperature of about 50xc2x0 C.
The present invention includes an iridium carbene complex of the formula [Ir(cod)(py)(SIMes)]PF6.; the complex can be prepared by a simple ligand exchange reaction of [Ir(cod)(py)2]PF6 with SIMes in toluene. Preferably, an excess of SIMes is used. The SIMes can be prepared and used in situ by the reaction of SIMes.HCl with KOBut in THF, and the free carbene is extracted with toluene and treated with [Ir(cod)(py)2]PF6 directly. This complex can be used as a catalyst in a hydrogenation reaction for hydrogenating simple olefins.
The reaction can occur at a pressure of 0.1 to 150 atm and a temperature of 0 to 150xc2x0 C. For example, the reaction can occur at a pressure of about 1 atm and a temperature of about 50xc2x0 C.
The present invention comprises an olefin hydrogenation catalyst bearing a nucleophilic carbene ligand. This catalyst can be used as a catalyst in a hydrogenation reaction to hydrogenate simple olefins. This hydrogenation can occur with H atom sources other than hydrogen gas. For example, the hydrogenation can comprise transfer hydrogenation; in such a case, alcohol can be the source of H atoms.
The present invention also comprises a complex of the formula [Ir(cod)(py)(L)]PF6, where L is from the group consisting of: IMes, 1,3-bis(2,4,6-trimethylphenyl)-imidazol-2-ylidene; IPr, 1,3-bis(2,6-di-iso-propylphenyl)-imidazol-2-ylidene; ICy, 1,3-bis(cyclohexyl)-imidazol-2-ylidene; and chiral carbene. This complex can be used as a catalyst for transfer hydrogenation reactions. This complex can be used as a catalyst in a method of hydrogenating simple olefins. The hydrogenation reaction can occur at a pressure of 0.1 to 150 atmosphere and a temperature of 0-150xc2x0 C.; for example, the reaction can occur at a pressure of about 1 atm and a temperature of about 50xc2x0 C. L can be ICy, 1,3-bis(cyclohexyl)-imidazol-2-ylidene.
The present invention also includes an iridium carbene complex of the formula [Ir(diene)(N-L)]X. where: diene is a diene or two monoene; N is a 2 electron nitrogen donor from the group consisting of oxazolines, phosphines, and carbenes; L is a bulky nucleophilic carbene; X is an anionic counterion; and N and L are tethered so N and L make a bidentate ligand. The two fragments can be tethered using a variety of subunits as known in the art. N can be an oxazoline so N-L is an oxazoline-carbene ligand; or N can be a phosphine so Nxe2x80x94L is an phosphino-carbene ligand, or N can be a carbene and N-L is a bis-carbene ligand. A chiral version of the complex can be used as a catalyst in a method of catalyzing asymmetric hydrogenation reactions.
The present invention also can be characterized as an iridium carbene complex of the formula [Ir(diene)(R-C)]X. where: diene is a diene or two monoene; Rxe2x80x94C is a chelating ligand; R is from the group consisting of phosphorus donors, oxygen donors, and nitrogen donors; C is a carbene; and X is an anionic counterion. R-C can be a chelating ligand from the group consisting of carbene-carbene, phosphine-carbene, and oxazoline-carbene. This complex can be used as a catalyst in a method of catalyzing hydrogenation reactions. The hydrogenation can be performed asymmetrically with a chelating ligand bearing a chiral center. The chelating ligand bearing a chiral center can be, for example, from the group consisting of chiral oxazoline-carbene, chiral phosphine-carbene, chiral carbene-oxazoline, chiral carbene-phosphine and chiral carbene-chiral carbene.